Serum and urinary indium as early biomarkers of airway dysfunction in indium-exposed workers

To investigate the relationships between indium exposure biomarkers and pulmonary injury markers among indium-exposed workers, and to evaluate the exploratory diagnostic utility of indium levels for identifying subclinical ventilatory abnormalities.

This cross-sectional study recruited 30 workers from a Taiwanese indium-tin oxide (ITO) facility. Participants completed standardised questionnaires, spirometry, diffusing capacity (diffusing capacity of the lungs for carbon monoxide) testing and chest radiography. Serum indium (In-S) and urinary indium (In-U) concentrations were quantified alongside pulmonary biomarkers (Krebs von den Lungen-6 (KL-6), Surfactant Protein A (SP-A), Surfactant Protein D (SP-D)) and systemic inflammatory and oxidative stress markers (Lactate Dehydrogenase (LDH), Malondialdehyde, C-Reactive Protein, 8-hydroxy-2-deoxyguanosine). Group comparisons were stratified by In-S level and workstation. Associations were assessed using Spearman's correlation. Receiver operating characteristic (ROC) analyses were performed to explore the diagnostic performance of indium biomarkers.

Production workers had significantly higher In-S and In-U levels than administrative staff (p<0.001). KL-6 and LDH were elevated in the high In-S group (p<0.01). In-S and In-U correlated moderately with KL-6 (ρ=0.556 and 0.536, respectively; p<0.001), and with SP-D (ρ=0.388 and 0.384; p=0.013 and 0.014). In-U showed negative correlation with SP-A (ρ=-0.329, p=0.038) and positive correlation with LDH (ρ=0.317, p=0.046). ROC analysis demonstrated exploratory diagnostic performance within this cohort of In-S for identifying reduced maximal mid-expiratory flow and reduced FEV₁/FVC ratio.

In-S and In-U levels are associated with biological markers of alveolar epithelial injury and functional parameters related to airway physiology. These findings support the potential role of indium biomonitoring in occupational surveillance, while underscoring the need for cautious interpretation given the cross-sectional design and limited sample size.